1. Field of the Invention
This invention relates to a circular direction vibrator in which a piezoelectric bimorph type vibrator is employed.
2. Description of the Prior Art
A piezoelectric bimorph type vibrator is known comprising a bimorph cell composed of a piezoelectric ceramic member and a metal plate attached thereto for converting a vibration in a lengthwise direction to a mechanical vibration in a direction of thickness of the bimorph utilizing the characteristic of the piezoelectric ceramic which is vibrated in a lengthwise direction when a voltage is applied thereto. There has also been provided a piezoelectric bimorph type vibrator in which the conversion of electrical energy into mechanical vibration in a direction of thickness of the bimorph can be obtained by attaching two piezoelectric ceramic members together so that the elongation and contraction directions of one of the members are opposite to those of the other of the members when a voltage is applied to the members causing each of the members to alternately elongate and contract. In either case, the piezoelectric ceramic member is obtained by subjecting ferroelectric ceramics capable of spontaneous polarization to polarization treatment (poling) which comprises applying high voltage to ferroelectric ceramics so as to induce one polarization direction therein. The polarization treatment has been effected merely for the purpose of inducing a single polarization direction in a single ceramic body.
Since the vibrating action of the conventional piezoelectric bimorph type vibrators is a simple bending motion produced when a voltage is applied thereto, the use of the conventional piezoelectric bimorph type vibrators producing such a bending motion as a vibration source is limited to electroacoustic transducers and piezoelectric filters, for example.
In general, the conventional piezoelectric vibrators have limited vibration modes in a direction of thickness and in a diametrical direction and these vibration modes are usually used as a direct drive.